Television system



Oct. 31, 1939. v. K. ZWORYKIN ET AL 2,178 0 3 TELEVISION SYSTEM Filedlarch 10, 19:52

I I 9 k 1 18 l l l a4 i "42 Generator- Generator f'orsam- Toorh For-saw-Tool J V currerzr wave ,4 urrenr wa ve Rad i 0 58 .52 5,000 10Transmitter ll AA/AAA- D H v v v v v v 6 8 1 E 'V 40 70 W\! vvvv/ :5 66E; ==V52 9 Generator Genemfor For-5171a Wave ForS/rze Wave 07000 10 70 IPhase Freouelzcy Shifter Doubler- INVENTOE'S. Vladzmzrl'. Z wor ylfm,Flume Fre uency Gregory 0g 11723121], 3 H177 Doubler 82 CJ 0 l3 ATTORNEPatented st. i958 PATENT OFFICE TELEVISION SYSTEM Vladimir K. Zworykin,Haddonfleld, and Gregory N. Ogloblinsky, Collingswood, N. J., assignorsto Radio Corporation of America, a corporation of Delaware ApplicationMarch 10, 1932, Serial No. 597,898

5 Claims.

Our invention relates to television systems, and more particularly tosystems of the type includ- 11:55 an electron tube for developingpicture sign In using television transmission tubes of the general typedisclosed in Patent No. 1,773,980 of August 26, 1930, to Philo T.Farnsworth, an image of the object is projected onto a cathode platecoated with light-sensitive material. A beam of. electrons is therebydeveloped, in which the electrons move with considerable velocity fromthe cathode plate to an anode plate having a central aperture back ofwhich an anode element is supported. The degree of electron emission atany instant from a particular elemental area of the cathode plate isdependent directly upon the light intensity at that instant on thiselemental area. For the purpose of preventing dispersion of. theelectrons in their travel from the cathode plate to the anode plate, afocusing coil is disposed about the tube and operates to develop amagnetic focusing field having lines of force extending in a directiongenerally axially of the tube.

Scanning is accomplished by so deflecting the entire electron beam bothhorizontally and vertically that the electrons from the elemental areas,in a transverse section of the beam at the anode plate, passsuccessively through the central aperture to the anode element referredto. Picture signals are thereby developed and supplied to suitableapparatus for transmission.

It has been found expedient to deflect the beam electromagnetically, forwhich purpose horizontal and vertical deflection coils are used todevelop deflecting fields transverse to the focusing field. Theadvantages of the combination of electromagnetic focusing andelectromagnetic deflection, however, have heretofore been offset byseveral disadvantages. In the first place, the deflection of the beam,instead of being at right angles to the transverse electromagneticdeflecting fields, is at an oblique angle, the angular difierencedepending upon the relation between the intensities of the focusing anddeflecting fields. In the second place, the focusing is appre- (Cl.IVS-7.2)

disclosed in the patent referred to, and which is 15 effective todevelop picture signals for transmission. Such a tube comprises aphotosensitive cathode I2, upon which is projected an image of an objectHi being televised, the latter being illuminated by a suitable lightsource 16. In operation, electrons are emitted from the cathode l2 andmove at high velocity in the form of a beam l8 directed at an anodeplate which is maintained at a high positive potential with respect tothe cathode by a battery 22 or other potential source.

The anode plate is provided at the center thereof with a small aperture25, back of which is supported an anode element 26 connected as shown toone end of a resistance 28.

For the purpose of focusing the beam 118 on the plate 20, anelectromagnetic coil 30, supplied by a battery 32, is so disposed asshown about the tube, that the flux lines extend substantially parallelto the tube axis. The strength of the focusing electromagnetic field isso adjusted by a resistance 36 that the electrons emitted from anyelemental area of the cathode H, such as the area 36, normally come to afocus on the anode plate 20. That is, the electrons emitted from theelemental area 36, for example, travel at high velocity along pathsgenerally axially of the tube, and under the influence of the focusingelectromagnetic field come to a focus at the opposite, correspondingelemental area 38 of. the anode plate 20. The degree of electronemission at the instant from the photosensitive area 36 is a directfunction of the light intensity on this area at this instant. In likemanner, there is electron emission from each of the elemental areas ofthe cathode i2, the degree of emission depending directly upon the lightintensity on the particular area at the instant. The focusingelectromagnetic field is efiective to focus the electrons emitted'fromany elemental area on the anode Plate 20.

Scanning is accomplished by so deflecting the entire beam l8transversely in both horizontal and vertical directions that during eachpictureframe period the electrons at the individual elemental regions ina cross-section of the beam, taken at the anode plate 20, passsuccessively through the aperture 24 and strike the anode element 26.This action is effective to develop picture signals in the resistance26, and these are amplified and transmitted in the well known manner bya suitable amplifier and radio transmitter 46.

For the purpose of deflecting the beam is in the manner aforesaid,electromagnetic coils 42 and 44 operate to develop electromagneticfields wherein the flux lines are transverse to the tube axis. The coils42 are connected to the output of a suitable generator 46 which causes,for example, a saw-tooth current wave at five thousand cycles to passthrough these coils, the resultingfield operating to deflect the beam l8five thousand times a second, horizontally. The coils 44 are connectedto the output of. a suitable generator 48 which causes, for example, asawtooth current wave at ten cycles to pass through these coils, theresulting field operating to deflect the beam I8 ten times a second,vertically.

The combination of electromagnetic focusing and electromagneticdeflection of the beam l8 has well known advantages. There is, however,a serious disadvantage which will now be explained, for which purposeconsideration will be given to the electrons emitted from one of theindividual elemental areas of the cathode l2, such as the area 36. Asthe beam I8 is deflected, and when the ray IQ of electrons issuing fromthe elemental area 36 is in the position indicated by dash lines,whereat this ray is directed at the aperture 24, the electrons arefocused at the point 50, an appreciable distance in front of thisaperture. This causes the electrons from the particular area 36 to beout of focus in some degree with respect to the anode element 26.

The various rays of electrons, propagated from elemental areas on thecathode I2 further removed from the center thereof than the area 36,will be out of focus a greater degree with respect to the anode element26, during the scanning action. The result of this action is that thetransmitted picture has substantially less degree of detail around theoutside portion than at the central portion. The degree of focusing onthe aperture 24 may be made more uniform over the entire picture area bycausing the beam to be focused normally on a plane slightly to the rightof the anode plate 20, so that when the various electron rays aredeflected to be directed at the aperture 24, they are more nearly at afocus with respect to the anode element 26. This expedient, however, isa compromise, and does not provide for the best operating action in theway of picture detail.

For the purpose of avoiding the difficulty outlined above, we propose tosuperimpose upon the electromagnetic focusing field a corrective waveform whereby the point at which the electrons in any ray come to a focusis varied as the beam I8 is deflected, the resulting action being thatwhen any ray is deflected to the position whereat it is directed at theaperture 24, the electrons meet at a focus on the anode element 26. Forthis purpose, a resistance 52 and a condenser 54 are connected as shownto the output 01. the

'by an auxiliary electromagnetic coil 56 which is connected to theresistance-condenser combination 52, 64 through a suitable coupling tube58. The focusing field is thereby varied in a manner dependent upon thecharacteristic wave-shape of the electromagnetic field for horizontal deflection of the beam l8.

In like manner, another corrective wave form is superimposed upon thenormal focusing field by means of a resistance 60 and a condenser 62connected as shown to the output of the generator 48. For this purpose,a second auxiliary electromagnetic coil 64 is disposed about the tube l0and is connected to the resistance-condenser combination 60, 62 by asuitable coupling tube 66. The focusing fleld is thereby varied in amanner dependent upon the characteristic wave-shape of theelectromagnetic field for vertical deflection of the beam I 8.

In operation, the corrective wave forms operate automatically to varythe focusing fleld in a manner similar to the characteristic waveshapesof the horizontal and vertical deflecting fields so that, at any instantduring the scanning action, the electrons are focused on the aperture 24and the anode element 26 immediately back of the same. The correctiveelectrical waves in the coils 56 and 64 can be said to approximate inshape the integrals of the respective wave-shapes developed by thegenerators 46 and 48.

In systems wherein scanning is accomplished by passing sine wavesthrough the deflecting coils 42 and 44, modification is made as shown inFig. 2. In this case, the generator 68 develops a sine wave at flvethousand cycles, and the integral of this wave is obtained, as anapproximation, by doubling the frequency by means of a suitablefrequency doubler 10. It is proposed to use a suitable phase shifter 12to compensate for a possible discrepancy in phase incident to the use ofthe frequency doubler 10. The auxiliary coil 56 is connected to theoutput of the phase shifter 12 through a suitable coupling tube 14.

The corrective wave form is developed and supplied to the auxiliary coil64 by a similar and operate to vary the focusing in such manher that, atany instant during the scanning action, the electrons are focused on theaperture 24 and the anode element 26.

In lieu of using independent auxiliary coils 56 and 64, the correctivewave forms may be superimposed on the normal focusing fleld byinduction, as shown in Fig. 3. In such case, suitable transformers 84and 66 are connected as shown between the coupling tubes and theexciting circuit for the focusing coil 36.

We claim as our invention:

1. In electron apparatus of the character described, anode structureprovided with an aperture, an anode element supported on one side ofsaid structure and in proximity to said aperture, photosensitive cathodestructure supported on the other side of said anode structure and inspaced relation with respect thereto, means for focusing an image onsaid cathode structure to develop a beam of electron rays directed atsaid anode structure, means for focusing said beam on said anodestructure, means for deflecting said beam in scanning fashion withrespect to said aperture, and means controlled by said deflecting meansand operating to vary the point of focus of the individual rays to apoint substantially at said aperture.

2. The combination with electron apparatus of the character describedcomprising a tube, electrodes supported in said tube in spaced relationwith respect to each other, said apparatus being characterized by thefact that in operation a beam of electrons is developed at one of saidelectrodes and is directed at the other electrode, means for deflectingthe electrons, and an electromagnetic coil disposed about said tube andcoaxially therewith for developing an electromagnetic field; of anauxiliary electromagnetic coil disposed about said tube and co-axiallytherewith for developing an electromagnetic field superimposed upon saidfirst-named field, and means controlled by said deflecting means andoperating to cause an electrical wave to pass through said auxiliarycoil.

3. The combination with electron apparatus of the character describedcomprising a tube, electrodes supported in said tube in spaced relationwith respect to each other, said apparatus bein characterized by thefact that in operation a beam of electrons is developed at one of saidelectrodes and is directed at the other electrode, means for deflectingthe electrons, and an elec trcmagnetic coil disposed about said tube andco-axially therewith for developing an electromagnetic field forfocusing the beam of electrons with respect to said other electrode; ofmeans controlled by said deflecting means and operating to develop asecond electromagnetic field superimposed upon the focusing field.

4. The combination with electron apparatus of the character describedcomprising a tube, electrodes supported in said tube in spaced relationwith respect to each other, said apparatus being characterized by thefact that in operation a beam of electrons is developed at one of saidelectrodes and is directed at the other electrode, electromagnetic meansfor focusing said beam with respect to said other electrode, andelectromagnetic means for deflecting said beam in scanning fashion withrespect to said other electrode; of means controlled by said deflectingmeans and operating in turn to control the focusing action of saidfirst-named electromagnetic means in such manner that during deflectionthe focus of the electrons at a fixed elemental zone at said otherelectrode is maintained.

5. The combination with electron apparatus of the character describedcomprising a tube, electrodes supported in said tube in spaced relationwith respect to each other, said apparatus being characterized by thefact that in operation a beam of electrons is developed at one of saidelectrodes and is directed at the other electrode, means for developingan electromagnetic field for focusing said beam on said other electrode,

' means for developing an electromagnetic field for deflecting said beamhorizontally, and means for developing an electromagnetic field fordeflecting said beam vertically; of means for superimposing on thefocusing field a wave form dependent upon the characteristic wave formof the horizontal deflecting field, and means for superimposing on thefocusing field a wave form dependent upon the characteristic wave formof the vertical deflecting field.

VLADIMIR K. ZWORYK'IN. GREGORY N. OGLOBIINSKY.

